Mating Behavior
Grooming Behavior and Cooperative Altruism
According to Kleinman et al (2003), capuchins have a polygynous mating system. Capuchins practice resource defense polygyny, as female capuchins benefit from the female-bonded groups that form and choose a home range which provides them with ample resources and predator protection. However, a common effect of being a resource defense polygynous group is that the males in the group compete for females, but in the case of the capuchin, females actively solicit the males (Case, 2005).
Breeding occurs throughout the year, but is more frequent during the dry seasons (spring and summer). Capuchins give birth every 2 years if the offspring survives and every year if it does not (Robinson and Janson, 1987). This is because female capuchins are the sole parental figures for their offspring and also because of the long dependence offspring have on their mothers. Thus, mothers are unable to care for more than one offspring during the breeding season. As a result, allomothering is a common practice among the capuchin monkeys, as all of the females within a group care for each other’s offspring (Byrne and Suomi, 1995).
Females are in estrus for 21 days with no visible genital swelling to signify that she is in estrus (animaldiversity.ummz.umich.edu). To make up for the lack of visible swelling, a female capuchin in estrus attracts the attention of the dominant male by following him and making loud calls in his direction. Only one female is in estrus at a time and males hardly ever fight over her yet female capuchins prefer to mate with the dominant male, mating with subordinate males when the dominant male is not available (Robinson and Janson, 1987; animaldiversity.ummz.umich.edu). Interestingly, the dominant male does not guard the estrus female, but is the one individual in the group to accomplish great mating success (Robinson and Janson, 1987).
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A female white-faced capuchin on the lookout for males to solicit.
Photo courtesy of: Richard Seaman©
The mating system among the capuchins is noteworthy, as it entails female solicitation of the male during her estrus. This solicitation behavior begins with the soliciting females directing grimaces and eyebrow raises towards a male, most likely the dominant male of the group, along with squeals or whines (Linn, Mase, LaFrancois, O’Keefe and Lifshitz, 1995; Welker, Höhmann, Schäfer-Witt, 1990; Redican, 1975). At this point, the male either responds negatively or positively, a reaction visible through his facial lip-smacking expression (Redican, 1975). The male either ignores the solicitation (negative response) or answers the female’s solicitation with his own grimaces and squeals. If the female receives a positive response from her desired male, the two will engage in a progression of “approach, run away, chase” behaviors while continuing their facial expressions and eyebrow raising. The dominant male is on the receiving end of these solicitations especially during the first couple of days of a female’s behavioral estrus, as that is the time in which she is most likely to conceive (Linn et al). Robinson and Janson (1987) suggest that during the first 3-4 days of a female’s estrus cycle, she actively solicits copulations from the dominant male and solicits subordinate males at the end of her estrus cycle if unsuccessful in mating with the dominant male. During the final days of her estrus cycle, the dominant male is very protective of “his” female, keeping her from mating with other males. This ensures that the dominant male’s genes will be the genes in the offspring, increasing the fitness viability of her offspring. Thus, Linn et al. hypothesized that female-female reproductive competition is quite intense, as mating with the dominant male ensures increased access to resources.
The number of solicitations between females and subordinate males and females and the dominant male are surprisingly the same, which suggests that the solicitations given out by the females do not necessary correlate with ovulation. Thus, it is estimated that copulations with subordinate males occur when the females are least fertile (Linn et al.) However, Linn et al. found that the amount of aggression during solicitation is closely related to female dominance rank among the group. Higher ranking females were more aggressive in their solicitations and received a greater frequency of gestures in comparison to lower ranking females (Linn et al.). This dominance did not correlate with overall rates of copulation, as both subordinate and dominant females copulated with a comparable amount of males. Yet, dominant females are more likely to mate with dominant males, as subordinate males rarely respond positively to dominant female mounts out of fear of aggressive behavior from the alpha male (Linn et al.).
Welker, Höhmann and Schäfer-Witt (1990) established their own colony of wild-born tufted capuchin monkeys to assess their courtship behavior. Their results conflict with those found by Linn et al, as they found that subordinate males are involved in more copulations than expected on the basis of the frequency of female courtship behaviors directed towards them. Welker et al explain this difference with three possible hypotheses. The first is that subordinate males could be less reluctant to accept a solicitation invitation to copulate and therefore copulate quickly with no chasing behavior. Secondly, the females could not court as many subordinates out of fear of losing their chance to mate with the dominant male. Interruptions while copulating have not been observed among the capuchin monkey, so it is unlikely that a female would cease copulating with a subordinate male if given the chance of copulating with the alpha male. Lastly, Welker et al suggest that dominant females are more aggressive in preventing subordinate females from courting males.
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From the active solicitation by females, it is apparent that the capuchin monkey has a promiscuous mating system. As a result, paternity is often unknown as female capuchins have been known to mate with more than one male (Kleinman et al, 2003). This is not necessarily hierchical promiscuity, as no research suggests that there is inter-species mating. Female capuchins solicit males within their own group, preferentially the dominant male. However, subordinate females mate with the dominant male relatively the same amount as the dominant female mates with the dominant female, thus there is no aggressive competition for mates. This is also because female are only in estrus once a year (if that), decreasing the amount of available females. In essence, it is reverse hierchical promiscuity, as females try to mate with as many males as possible, ensuring a pregnancy. Since there are multiple males in the group, females have the opportunity to mate with numerous males, forming promiscuous relationships. Hierchical promiscuity is possible among the capuchins, as females are the sole caregivers of the offspring, only asking for males to babysit when other females are not available. Nevertheless, since females solicit males, promiscuous mating is a possibility (Robinson and Janson, 1987).